Sunday, Nov. 29, 2009 | It’s a lonely world for the two northern white rhinos at Escondido’s Wild Animal Park. They are among less than a dozen of their kind left on Earth.
Conservationists work constantly through habitat protection and other means to save these and other endangered species. And now they are adding a new technology to their list of possible solutions to extinction — stem cells.
Scientists at the San Diego Zoo’s Institute for Conservation are working on two separate projects that employ some of the same stem cell breakthroughs that might someday treat disorders like Alzheimer’s and Parkinson’s diseases in humans.
“This is a very preliminary experiment,” said Oliver Ryder, director of genetics at the Institute for Conservation Research. “We want to see if the process that’s worked on human cells will work in animals.”
Ryder’s group wants to reprogram adult cells from drill monkeys and northern white rhinos into stem cells. Using a type of virus called a retrovirus, scientists introduce genes into the DNA of an adult cell that cause it to behave like an embryonic stem cell, a versatile cell that can divide to form any other cell type in the body.
The Zoo researchers are working in collaboration with world-renowned stem cell researcher Jeanne Loring and her lab at the Scripps Research Institute.
Exactly how or when science might use cell reprogramming technology in animals isn’t yet clear. If this new application for stem cells succeeds, however, it could potentially be used to replace or regrow damaged tissues in animals, just as in humans.
Scientists could also clone an animal by injecting the stem cells into very early-stage embryos, and implanting them into a surrogate mother from a closely related species.
Reprogrammed stem cells are today’s hottest topic in the world of stem cell research. Some researchers say the ability to convert adult cells into stem cells could lead to breakthroughs far sooner than they’d originally believed.
But the process also has its risks. Retroviruses sometimes can cause a cell to become cancerous. Researchers are working now on ways to deal with this problem.
And the San Diego Zoo has an additional resource that could help detect defects in the reprogrammed cells. The institute is home since the 1970s to the Frozen Zoo, one of the largest animal biobanks in the world. The Frozen Zoo stores DNA and tissue samples from more than 8,400 individual animals — a Noah’s Ark on ice that plays an ever-expanding role in conservation.
When it comes to reprogramming stem cells, the Frozen Zoo gives scientists another way to screen for problems. By comparing the chromosomes in the reprogrammed cells to normal chromosomes from the same species, scientists can check for certain kinds of abnormalities — and hopefully reduce the possibility of defects.
Cloning, Then and Now
The San Diego Zoo has participated in a couple of attempts to clone endangered species in the past; a banteng at the Wild Animal Park was successfully cloned in 2003. The older and more common methods of cloning, however, are extremely inefficient. Producing Dolly the sheep, for example, took hundreds of attempts.
Stem cells could provide an easier and more efficient method of cloning. Cloning can’t save endangered animals from serious threats like habitat loss or poaching, but it could assist in breeding efforts by duplicating valuable animals in a zoo’s collection or cloning from cells of dead animals stored in biobanks like the Frozen Zoo.
Recent breakthroughs have made cloning using stem cells a more viable proposition. Earlier this year, Chinese scientists cloned mice by reprogramming skin cells from the mice into stem cells. Scientists could potentially clone dead animals of an endangered species with the same technique, using the tissue samples and cell cultures stored at the Frozen Zoo.
While a few researchers elsewhere have talked about the possibility of resurrecting long-dead creatures like the woolly mammoth, Ryder and the San Diego Zoo aren’t interested in those kinds of projects.
“We focus on reducing the risk of extinction for species that are here now, as opposed to bringing back species that are extinct,” Ryder said.
Stem cell research and cloning in endangered animals is largely free from the bitter controversy that surrounds similar research in humans. Many environmentalists see no problem with these kinds of efforts — as long as they don’t distract from conservation or give people the impression that cutting-edge technology can replace preservation of natural habitat, said Jim Peugh, conservation chair at the San Diego Audubon Society.
“If we can keep something alive in a zoo, in a lab, why try to preserve it in the wild? We worry that people could come to that conclusion,” Peugh said.
Zoo researchers agree that saving wildlife is the goal. But for those species whose habitat is disappearing or that are dwindling rapidly in numbers, advances in genetics and breeding technology could offer improved odds at survival.
Saving Condor Sperm
Another group of scientists at the Zoo’s conservation institute has found a different use for stem cell science in animals. Rather than reprogramming adult cells into stem cells like Ryder’s team, they’ve transferred male germline stem cells — stem cells that divide to form sperm in the testes — from adult quail to embryonic chickens.
Once these chickens reach adulthood, they become cross-species sperm donors, producing not only chicken sperm but quail sperm as well. “We can take germ cells from an animal who has never reproduced or is too old to reproduce and produce sperm,” said Barbara Durrant, director of reproductive physiology at the institute.
These methods even offer researchers the potential to produce sperm from valuable birds in the collection even after they are dead. The researchers can collect germ cells after the animal has died, culture them and preserve them, Durrant said.
While Durrant’s group is developing the technique in quail and chickens, ultimately they want to work with endangered birds such as the California condor. Like the institute’s other research projects, this technique might eventually play a role in captive breeding programs — programs that are often vital for species extinct in the wild.
And with pressures mounting on shrinking populations of wildlife around the globe, Ryder, says simply: “This is the challenge of our time.”
Jonathan Parkinson is a San Diego-based freelance writer. Please contact him directly at email@example.com with your thoughts, ideas, personal stories or tips. Or set the tone of the debate with a letter to the editor.